The present invention relates to di- and tri-peptidic derivatives comprising the pharmacophore Dmt-Tic and related compositions and methods of use in the antagonism and agonism of xcex4 and xcexc opioid receptors and in the inhibition of P-glycoprotein, specifically hMDR-1.
Endogenous opioids are believed to be involved in the modulation of pain perception, in mood and behavior, learning and memory, diverse neuroendocrine functions, immune regulation and cardiovascular and respiratory function. Opioids also have a wide range of therapeutic utilities, such as treatment of opiate and alcohol abuse, neurological diseases, neuropeptide or neurotransmitter imbalances, neurological and immune system dysfunctions, graft rejections, pain control, shock and brain injuries.
There are believed to be three types of opiate receptors, namely xcex4, xcexa and xcexc. Genes encoding these three main receptor types now have been cloned. Sequencing of the cloned opioid receptor genes has revealed a substantial degree of amino acid homology between different receptor types (Meng et al., PNAS USA 90: 9954-9958 (1993); Thompson et al., Neuron 11: 903-913 (1993); Evans et al., Science 258: 1952-1955 (1992); and, Kieffer et al., PNAS USA 89: 12048-12052 (1992)), which explains the tendency of opioid receptor ligands, even those reported to be selective, to bind to more than one type of opioid receptor. Based on differences in the binding profiles of natural and synthetic ligands, subtypes of opioid receptors have been suggested, including xcexc1 and xcexc2 (Pasternak et al., Life Sci. 38: 1889-1898 (1986)) and xcexa1 and xcexa2 (Zukin et al., PNAS USA 85: 4061-4065 (1988)). Different subtypes of a given type of opioid receptor may co-exist in a single cell (Evans et al. (1992), supra; and Kieffer et al. (1992), supra).
The xcexc opioid receptor in the brain appears to mediate analgesia (Kosterlitz et al., Br. J. Pharmacol. 68: 333-342 (1980)). It is also believed to be involved with other undesirable effects, such as respiratory depression (Ward et al., Soc. Neurosci. Symp. 8: 388 (abstract) (1982)), suppression of the immune system (Plotnikoff et al., Enkephalins and Endorphins: Stress and the Immune System, Plenum Press, NY (1986); Yahya et al., Life Sci. 41: 2503-2510 (1987)) and addiction (Roemer et al., Life Sci. 27: 971-978 (1981)). Its side effects in the periphery include inhibition of intestinal motility (Ward et al., Eur. J. Pharmacol. 85: 163-170 (1982)) and secretion in the small intestine (Coupar, Br. J. Pharmacol. 80: 371-376 (1983)).
xcex4-opioid receptors also mediate analgesic but are not involved in addiction. They may have an indirect role in immune suppression.
There appears to be a single binding site for agonists and antagonists in the ligand-binding domain of xcex4 receptors. Thus, the xe2x80x9cmessage domainxe2x80x9d of xcex4-agonists and xcex4-antagonists probably presents a similar low energy conformer in order to fit the receptor cavity. The minimum size of that xe2x80x9cmessage domainxe2x80x9d constitutes the dimensions of a dipeptide (Temussi et al., Biochem. Biophys. Res. Commun. 198: 933-939 (1994); Mosberg et al., Lett. Pept. Sci. 1: 69-72 (1994); and Salvadori et al., J. Med. Chem. 42: 3100-3108 (1997.)), which has a specific spatial geometry in solution (Bryant et al., Trends Pharmacol. Sci. 18: 42-46 (1998); Bryant et al., Biol. Chem. 378: 107-114 (1997); Crescenzi et al., Eur. J. Biochem. 247: 66-73 (1997); and Guerrini et al., Bioorg. Med. Chem. 6: 57-62 (1998)) as seen in the crystallographic evidence for TIPP analogues (Flippen-Anderson et al., J. Pept. Res. 49: 384-393 (1997)) and N,N(Me)2-Dmt-Tic-OH.
The Dmt-Tic pharmacophore represents a distinct class of xcex4-opioid antagonists (Salvadori et al., Mol. Med. 1: 678-689 (1995); Bryant et al. (1998), supra; and Lazarus et al., Drug Dev. Today 1998: 284-294). Observations of differences between the xcex4 opioid receptor binding of Dmt-Tic peptides and their Tyr-Tic cognates (Salvadori et al. (1995), supra; Lazarus et al. (1998), supra; and Lazarus et al., Int""l Symp. on Peptide Chem. and Biol., Changchung, PRC (1999)) indicates that Dmt assumes a predominant role in the alignment or anchoring of the peptide within xcex4, xcexc and xcexa opioid receptor binding sites (Bryant et al. (1998), supra; and Bryant et al. (1997), supra; Crescenzi et al. (1997), supra; and Guerrini et al. (1998), supra) or affects the conformation of the dipeptide antagonists in solution (Bryant et al. (1997), supra; and Crescenzi et al. (1997), supra). Furthermore, observations of differences between the spectra of activity exhibited by the Tyr-Tic cognates of certain Dmt-Tic peptides (Schiller et al., PNAS USA 89: 11871-11875 (1992); Schiller et al., J. Med. Chem. 36: 3182-3187 (1993); Schiller et al., Peptides Hodges and Smith, eds., ESCOM (1994); pp. 483-486; Temussi et al. (1 994), supra; Mosberg et al. (1994), supra; Salvadori et al. (1995), supra; Lazarus et al. (1998), supra; and Lazarus et al. (1999), supra) and the corresponding Dmt-Tic peptides suggests that the C-terminal xe2x80x9caddressxe2x80x9d portion of the peptide can influence the xe2x80x9cmessage domain.xe2x80x9d
Recently, cyclic peptides and di- and tri-peptides comprising the pharmacophore Dmt-Tic have been developed and have been shown to exhibit high selectivity, affinity and potency for the xcex4-opioid receptor. Such peptides have been shown to function as either agonists, partial agonists, antagonists, partial antagonists or mixed antagonists/agonists for opioid receptors (see Lazarus et al., U.S. Pat. No. 5,780,589, and Schiller, U.S. Pat. No. 5,811,400).
The uniqueness of the xcex4 receptor has led to the use of moderately xcex4-selective alkaloid antagonists in clinical trials, such as for the amelioration of the effects of alcoholism (Froehlich et al., Alcohol. Clin. Exp. Res. 20: A181-A186 (1996)), the treatment of autism (Lensing et al., Neuropsychobiol. 31: 16-23 (1995)), and Tourette""s syndrome (Chappell, Lancet 343: 556 (1994)). The xcex4-opiate antagonist naltrindole (Portoghese et al., Eur. J. Pharm. 146: 185-186 (1998)) has been shown to inhibit the reinforcing properties of cocaine (Menkens et al., Eur. J. Pharm. 219: 346-346 (1992)), to moderate the behavioral effects of amphetamines (Jones et al., J. Pharmacol. Exp. Ther. 262: 638-645 (1992)), and to suppress the immune system (Jones et al. (1992), supra) for successful organ transplantation (House et al., Neurosci. Lett. 198: 119-122 (1995)) in animal models (Arakawa et al., Transplant Proc. 24: 696-697 (1992); Arakawa et al., Transplant 53: 951-953 (1992); and Arakawa et al., Transplant. Proc. 25: 738-740 (1993)). The same effects also have been shown for 7-benzylspiroindanylnaltrexone (Lipper et al., Eur. J. Pharmacol. 354: R3-R5 (1998)).
The intractable membrane barriers, such as the blood-brain barrier (BBB), must be circumvented in order for peptide antagonists to express activity in vivo (Ermisch et al., Physiol. Rev. 73: 489-527 (1993)). The requisite physicochemical properties of compounds capable of passing through this barrier include low molecular weight ( less than 800 Da) and high octanol-water coefficient characteristics.
In view of the above, the present invention seeks to provide more potent xcex4-opioid antagonists and xcex4-opioid antagonists with high dual binding affinity and biological activity toward xcex4-opioid and xcexc-opioid receptors.
In addition to the above, one of the major chemical determinants for the inhibition of hMDR-1 involves the presence of strong hydrophobic substituents necessary for lipid solubility (Ford et al., Cancer Res. 50: 1748-1756 (1990); Zamora et al., Mol. Pharmacol. 33: 454-462 (1988); and Nogae et al., Biochem. Pharmacol. 38: 519-527 (1989)) as constituted by saturated and aromatic rings, as well as a tertiary nitrogen (Zamora et al. (1988), supra; Ramu et al., Int. J. Cancer 43: 487-491 (1989); and Pearce et al, PNAS USA 86: 5128-5133 (1989)). In addition to a role in drug resistance, the human Pgp-1 protein is expressed in a variety of normal human tissues and plays an important physiological role in maintenance of the BBB (Schinkel et al., J. Clin. Invest. 97: 2517-2524 (1996); Schinkel et al., Int. J. Clin. Pharmacol. Ther. 36: 9-13 (1998); and Jonker et al., Br. J. Pharmacol. 127: 43-50 (1999)). In the BBB, Pgp activity in apical membranes of the capillary endothelial cells functions to at least partially exclude a wide variety of hydrophobic toxicants from the brain (Zamora et al. (1988), supra; Schinkel et al. (1996), supra; and Jonker et al., Br. J. Pharmacol. 127: 43-50 (1999)). These include some drugs with central nervous system activities, such as certain opiate alkaloids and analogues thereof (Callaghan et al., J. Biol. Chem. 268: 16059-16064 (1993)). Thus, the present invention also seeks to provide inhibitors of hMDR-1.
These and other objects of the present invention, as well as additional inventive features, will be apparent to the ordinarily skilled artisan from the detailed description provided herein.
The present invention provides a compound of formula: 
wherein Rxe2x80x2 is selected from the group consisting of
H2Nxe2x80x94,
H2NH2Cxe2x80x94, 
Rxe2x80x3 is selected from the group consisting of
xe2x80x94CH2COOH,
xe2x80x94COOH,
xe2x80x94CONHNH2, 
xe2x80x94COxe2x80x94Alaxe2x80x94NHCH3, 
Also provided by the present invention is a composition comprising at least one compound of the above formula.
The present invention further provides methods of treatment. In one embodiment, a method of treating a mammal in need of an antagonist of a xcex4-opioid receptor is provided. The method comprises administering at least one compound of formula: 
wherein (i) Rxe2x80x2 is H2Nxe2x80x94 and
Rxe2x80x3 is xe2x80x94CH2COOH,
(ii) Rxe2x80x2 is H2Nxe2x80x94 and 
Rxe2x80x3 is
(iii) Rxe2x80x2 is 
Rxe2x80x3 is 
(iv) Rxe2x80x2 is 
Rxe2x80x3 is 
(v) Rxe2x80x2 is H2Nxe2x80x94 and
Rxe2x80x3 is 
or (vi) Rxe2x80x2 is H2Nxe2x80x94 and
Rxe2x80x3 is 
in an amount that antagonizes a xcex4-opioid receptor in the mammal. In another embodiment, the present invention may provide a method of treating a mammal in need of an agonist of a xcex4-opioid receptor. The method may comprise administering at least one compound of formula: 
wherein (i) Rxe2x80x2 is H2Nxe2x80x94 and
Rxe2x80x3 is 
(ii) Rxe2x80x2 is H2Nxe2x80x94 and
Rxe2x80x3 is xe2x80x94CO-Alaxe2x80x94NHCH3 
in an amount that agonizes a xcex4-opioid receptor in the mammal. In yet another embodiment, the present invention may provide a method of treating a mammal in need of an agonist of a xcexc-opioid receptor. The method may comprise administering at least one compound of formula: 
wherein (i) Rxe2x80x2 is H2Nxe2x80x94 and
Rxe2x80x3 is 
(ii) Rxe2x80x2 is 
Rxe2x80x3 is 
or (iii) Rxe2x80x2 is H2Nxe2x80x94 and Rxe2x80x3 is xe2x80x94CO-Alaxe2x80x94NHCH3 in an amount that agonizes a xcexc-opioid receptor in the mammal. In still yet another embodiment, the present invention provides a method of inhibiting the binding of an opioid receptor-binding compound with a P glycoprotein in a mammal. The method comprises administering at least one compound of formula: 
wherein (i) Rxe2x80x2 is H2Nxe2x80x94 and
Rxe2x80x3 is 
(ii) Rxe2x80x2 is H2Nxe2x80x94 and
Rxe2x80x3 is 
(iii) Rxe2x80x2 is 
Rxe2x80x3 is 
(iv) Rxe2x80x2 is H2Nxe2x80x94 and
Rxe2x80x3 is 
(v) Rxe2x80x2 is H2Nxe2x80x94 and
Rxe2x80x3 is 
in an amount effective to inhibit the binding of an opioid receptor-binding compound with a P glycoprotein in a mammal.